In some communication networks, such as a public switched telephone network (PSTN), a callee may not determine whether an incoming call is voice data or fax data before the call is answered. As a result, traditional fax machines are often connected to a dedicated PSTN telephone line, which imposes added expense to procure and maintain the dedicated line. For fax machine users that opt to employ a fax machine without a dedicated PSTN telephone line, situations will arise in which a call is answered by the callee that results in hearing unpleasant fax tones generated by a fax caller. Typically, the callee will hang-up the telephone and let the fax machine answer the call under the assumption that the caller will attempt to re-transmit the fax call.
On the other hand, if the caller is gracious enough to precede the attempted fax transmission with a preliminary voice call, then the callee may know not to answer a subsequent call under the assumption that it was originated by the fax caller. The callee's fax machine, whether it is connected to a shared voice/data PSTN line, a dedicated PSTN line, or part of a unified messaging (UM) platform, may receive the call, detect fax tones, negotiate a connection with the caller fax device (e.g., a fax machine employing the T.30 protocol), and transmit the fax data.
Voice and/or fax data may be transmitted (in part or in whole) via an Internet protocol (IP). In such circumstances, media gateways are typically employed to, in part, interface between PSTN and IP networks, handle traffic switching, and/or detect and adapt to one or more media types (e.g., Time Division Multiplex, IP conversion(s), fax tone detection, etc.).
Communication networks typically assume a received call is of a voice type, in which case if upon processing a call, a media gateway discovers one or more fax tones, and the media gateway forwards the tones to a media gateway controller. The media gateway controller receives the fax tone(s) from the media gateway and determines appropriate instructions required for subsequent handling of the call. Each interface with the media gateway and or the media gateway controller also includes one or more call signaling message exchanges (e.g., SS7, H.248, SIP, etc.), which may cause congestion within the communication network.